1. Field of the Invention
The present invention relates to a spiral type fluid compressor which is, for instance, suitable for compressing a refrigerant of a cooling cycle.
2. Description of the Prior Art
As general compressors in the conventional practice, there are available a reciprocating type compressor, rotary type compressor, and a spiral type compressor where a refrigerant fed into an operation chamber from a suction end side of a cylinder is transferred successively into a discharge end of the operation chamber while being compressed, so as to be discharged into an external portion.
With reference to FIG. 1, the spiral type compressor comprises (1) a cylinder 105 rotated by drive means consisting of a stator 101 and a rotor 103 and (2) a rotary rod 109 which is disposed eccentrically relative to an axis of the cylinder 105 by a distance e and which is rotatable relative to the cylinder 105 through an Oldham mechanism 107. Spindle portions 111, 111 of the rotary rod 109 are freely rotatably supported by bearing portions 113, 113 provided at both ends of the rotation rod 109. A pair of spiral grooves 115, 115 is formed on an outer circumferential surface of the rotary rod 109. The pitches of the groove 115 are gradually reduced with a distance toward the both ends of the rotary rod. A spiral blade 117 is supported in a manner that the spiral blade 117 is freely movable in the radial direction. The outer circumferential surface of the spiral blade 117 is in contact with an inner circumferential surface of the cylinder 105 so that the spiral blade 117 rotates together with the rotary rod 109. The rotary rod 109 rotates eccentrically in a manner that a part of the outer circumferential surface of the rotary rod 109 is in linear contact with the inner circumferential surface of the cylinder 105, so that the spiral blade 117 moves radially relative to the spiral grooves 115. Thereby, there are formed a plurality of operation chambers 119 along an axial direction. With reference to FIG. 2, a volume of the operation chamber 119 is determined by a size of pitch P of the spiral blade 111 supporting the spiral blade 117. The volume of the operation chamber 119 formed by the spiral blades 117 becomes gradually smaller from a central portion toward both ends of the rotary rod, whereby the refrigerant fed to the operation chamber 119 from a suction pipe 121 through a suction hole 123 (FIG. 1) is successively transferred toward both ends so as to be gradually compressed and discharged finally to outside.
The refrigerant is compressed while being transferred from the central operational chamber 119 toward the right- and left-side operational chamber 119, so as to be discharged outside. Then, with reference to FIG. 3, there is caused load forces F, F in the vicinity of the both ends of the rotary rod 109 because a gaseous pressure thereof is high there. The force F is a load force caused by the compression of the gas.
Now, the gas load force F is received by the bearing portion 113. However, a supporting area a of the bearing portion 113 is located very far from the load point of the gas load force F. Moreover, when there is disposed the spiral oil pump 125 within the supporting area a shown in FIG. 3, the actual supporting area becomes a portion indicated with b in FIG. 3, which is about a half of the area a. Thus, the supporting area b is further away from the load point of the gas load force F. Thereby, the rotary rod 109 tends to be deformed as indicated with dotted lines shown in FIG. 3, so that the blade 117 forming the operational chamber 119 tends to be out of contact away from the inner circumferential surface of the cylinder 105 so as to cause a leakage. This leakage caused by the deformation is responsible for a significant decline of performance of the compressor. To alleviate such problem, the supporting shaft 111 of the rotary rod 109 may be made longer thus expanding the supporting area a in order to suppress the degree of deformation and improve the performance. However, the size of the compressor becomes undesirably large so as to cause other problems.